FORWARD ACTING, STAPLE MACHINE WITH PASSIVE RELEASE

Abstract: A manually powered fastening tool which stores and instantly releases the energy of a spring (40) such that it may force a staple (70) or other fastener into an object by an impact blow in which the operating handle (22) is hinged near the end of the tool body opposite the end from which the staples (70) exit. A staple ejecting plunger (21) is unstably linked to the spring (40) such that when a lever (28) moved by the operating handle (22) to energize the spring (40) slips past ledges (11, 13) thereby removing a light holding force, the lever (28) disengages from the spring (40), which releases the plunger (21). The tool housing (10) comprisses a cantilevered rear profile.

Description: FORWARD ACTING, STAPLE MACHINE WITH PASSIVE RELEASE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to manually powered fastening devices, and more specifically to impact driven staple guns and tacking machines. 2. Description of the Related Art The fastening tool of the present invention is similar to that disclosed in co-pending application Serial No. 07/899,748 and U.S. Patent No. 5,165,587. The fastening tool enables an operator's single hand to compress a spring to store and instantly release the energy of the spring to expel a staple from the fastening tool by an impact blow. The fastening tool incorporates a forward acting actuator lever. The staples exit towards the front end of the fastening tool while the lever is hinged near the rear end of the fastening tool. The tool may be gripped through an opening in the body of the tool. The opening extends to the front of the tool, and in certain configurations, the opening may originate at the front of the body of the tool. U.S. Patent No. 2,671,215 issued to Abrams discloses the familiar Arrow stapler. A lever is pivoted towards the front of the staple gun. Pressing down the lever behind the pivot compresses a coil spring and raises a plunger through a pivotally attached actuating arm. At a pre-deter ined point of the lever travel, the actuating arm has arced rearward sufficiently such that it releases the plunger assembly. The plunger is driven downwards by the force stored in the coil spring. The coil spring is located immediately adjacent to, or above, the plunger. The plunger is located in the front of the staple gun. U.S. Patent No. 3,610,505 issued to Males discloses a design similar to the Abrams design. A lever is pivoted near the front of a staple gun. Pressing the extended arm of the lever downwards towards the rear of the staple gun causes a coil spring to compress and simultaneously raises a plunger. Once the lever has been lowered past a predetermined point, • the lever is released from the coil spring and plunger assembly by the force of a cam assembly, and the force stored in the coil spring is allowed to drive the plunger downwards, striking and ejecting a staple. The plunger is located at the front of the staple gun. U.S. Patent No. 2,326,540 issued to Krantz discloses a staple gun in which the actuation lever is pivoted towards the rear of the staple gun. Through a series of levers, this action is connected to a coil spring and plunger located at the front of the staple gun. As the lever arm is lowered, the spring is compressed and the plunger is raised. A pivotable member of the spring and plunger assembly links the levers to the assembly. Once the lever reaches a predetermined point, the pivotable member is forcibly disengaged from the lifting lever, and the energy stored in the coil spring is allowed to release, driving the plunger downward, striking and expelling a staple. U.S. Patent No. 2,769,174 issued to Libert describes a staple gun in which the actuation lever is pivoted at a point towards the rear of the staple gun, and staples are expelled out of the front of the staple gun. Pressing down on the actuation arm towards the bottom of the staple gun actuates a series of levers and compresses a coil spring to raise the plunger. At a predetermined point, two of the levers are forcibly decoupled and the energy stored by the coil spring is allowed to release, driving the plunger downwards, striking and expelling a staple. U.S. Patent No. 4,629,108 issued to.Judge describes a staple gun contained within a stamped metallic frame which is enclosed in a second stamped or molded housing. Judge describes a common mechanism to accommodate an actuation lever pivoted near the rear of the staple gun. The release mechanism appears to be similar to that of Libert. U.S. Patent No. 3,862,712 issued to LaPointe et al. discloses a staple guiding track which slides rearward to expose a chamber in the staple gun body into which staples are placed. The staple gun is inverted during this operation. This sliding mechanism requires numerous components and assembly operations for its manufacture. U.S. Patent No. 4,452,388 issued to Fealy comprises a staple gun with an intermediately actuated leaf spring. The multi-layered leaf spring spans the length of the tool-body. A mechanism pulls upward upon the spring to lift the spring and plunger. The mechanism is then forced away from the spring to release the spring from the actuating mechanism. Typical of the prior art, the above described designs use either of two release methods. By one method a cam or stop acts upon a linking member to force a delinkage at the release position. By the other method a rotating actuating member is slidably linked to a reciprocating plunger member. At the release position the actuating member has rotated out of the plane of motion of the plunger member, and the plunger member is released. The above release methods may be called active or direct releases because the release is forcibly and directly caused by the actuating members. The first method requires a substantial increase in operating force to enable the forced release action. The second method provides only a vague release action since there is no secondary event to cause the release. No distinct action occurs at the release position. SUMMARY OF THE INVENTION The present invention incorporates a passive or indirect release into a forward acting, staple machine. A linkage between the operating lever and plunger becomes unstable near the release point. The unstable linkage is held in place by the light force from a further component. In a preferred embodiment, the further component is a ledge or tab extending inward from the tool housing wall to form a release surface. This release surface serves to slidably guide the unstable linkage with a force just great enough to hold the linkage together. At the release point the ledge or tab is no longer present to guide the linkage and the linkage separates. The passive release therefore uses a distinct secondary event to cause delinkage without requiring increased operating force. In one embodiment of the present invention the actuating lever engages a cantilevered tab extending from the spring. The spring comprises either a variable cross section flat torque transmitting spring or a coiled wire torsion spring. Those springs differ from the leaf spring taught in U.S. Patent No. 4,452,388 issued to Fealy, for example, in that they allow an efficient distribution of stress along the spring length with the use of only one component. The actuating system of the above embodiments differs from Fealy in that the engagement surface is a cantilevered, rearward facing tab; the tab is not part of the live spring. In a further embodiment of the present invention, the engagement tab is part of the plunger. The actuating lever and spring are linked through the plunger, with the linkage points substantially aligned across the width of the plunger. Rather than the usual forward to back release motion, the present design provides a sideways motion of the actuating lever to effect the release of the spring and plunger assembly. Such motion occurs by wobble about two attachment points of the actuating lever and hence requires no front to back sliding of the lever. The sideways wobble thereby reduces friction during the release action. The housing shape of the present invention provides two features to improve the function of the invention. One feature comprises an overhung or cantilevered back end. The upper rear portion of the housing extends back further than the lower rear portion. The cantilevered back end provides a more rearwardly hinged operating lever while reducing the material required for the housing, since only the upper rear portion extends back to accommodate the lever hinge. A further feature of the cantilevered back end is to communicate the direction to operate the tool. A back so shaped is unlikely to be mistaken for the front end. A second feature of the housing comprises an intermediate finger stop across the grip opening. The middle, or longest, finger may support the tool by- this finger stop, especially when the tool is used vertically. The middle finger has the greatest ability to extend the tool body away from the operating handle and the intermediate finger stop allows this action. The return spring serves two functions. First it provides the bias to return the operating handle. The spring provides a greater return bias in its extended position, with reduced bias in its most contracted position. The handle thereby exhibits a solid return action while the return spring causes the minimum possible resistance during operation of the tool. The second function of the spring is to control wobble of the engagement lever. It is therefore an object of the present invention to provide a spring actuated fastening device in which the spring is delinked from an actuating lever through a passive or indirect event. It is a further object of the present invention to provide a cantilevered profile at the lower rear of the tool housing to conserve material and communicate which end is the rear of the tool. It is still another object of the present invention to provide a means for the longest, middle, finger to support and control the weight of the tool. It is yet another object of the present invention to provide a fastening tool with a dual function return spring which gives a return bias to the operating lever and also controls release and engagement functions. It is still a further object of the present invention to provide a fastening tool in which the return spring features varying force to cause a maximum return bias only in the extended position, where it is most needed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side elevation of a fastening tool, with one half of the housing removed, with its grip handle in an extended position and spring in its rest state, as the tool would appear before commencing an operating sequence. Fig. 2 is a side elevation of the fastening tool of Fig. 1, with the grip handle fully drawn toward the tool body and spring energized as the tool would appear just prior to ejection of a staple. Fig. 3 is a side elevation of the fastening tool of Fig. 1, with the spring in its rest state and the handle fully drawn toward the tool body, as the tool would appear just after ejection of a staple. Fig. 4 is a side elevation view of the fastening tool of Figure 1, with the staple loading track drawn rearward to expose the staple loading channel. Fig. 5 is a view, partly in section, of the fastening tool of Figure 1, showing a portion of the tool housing, actuating lever and mainspring front portion. The lever is near the release position. Fig. 6 is the view of Figure 5, with the lever moved sideways to its release position, the spring shown in phantom in its uppermost position and in solid section in its lower position. Fig. 7 is the view of Figure 6, with the lever moved sideways past center, aligned so the lever may pass through the plane of the spring front end. Fig. 8 is the view of Figure 7, with the lever in an initial position below the spring. Fig. 9 is the section of the mainspring of Figures 5 through 8. Figs. 10 & 11 are plan and side elevations, respectively, of the complete spring of Figure 9. Figs. 12, 13 and 14 are end, side and plan elevations, respectively, of a plunger which mates with the spring of Figures 9 through 11. Fig. 15 is a view of a torsion spring alternative to the flat spring of Figs 9 through 11, engaging the plunger of Figures 12 through 14. Figs. 16, 17 & 18 are end, side and plan elevations, respectively, of a plunger according to a further embodiment. Fig. 19 is a plan elevation of an open ended flat spring. Fig. 20 is an elevation of the flat spring of Fig 19, mated with the plunger of Figures 16, 17 & 18. Figs. 21, 22 & 23 are side, front & bottom elevations, respectively, of a loading track. Figs 24 & 25 are top and side elevations of a staple feeder. DETAILED DESCRIPTION OF THE INVENTION Referring to Fig. 1, die-cast metal housing 10 consists of two opposing halves joined together to contain, guide and hold the internal components of the fastening tool in a predetermined position. Opening 14 in die cast housing 10 is provided to receive the index finger of a hand as it grips the fastening tool. Finger stop 17 provides a surface for the middle finger to support the tool when the tool is held vertically. Molded handle cover 62 provides a thumb rest surface 66 to accommodate the thumb of a user's hand. Pivot 52 is a post near the rear of housing 10 and is part of housing 10. Handle cover 62 fits over, and covers the top portion of, lever 22. Roller linkage 26 provides a frictionless connection between levers 22 and 28. Lever 28 pivots about pin 50. Pin 50 is identical to roller linkage 26. As lever 22 is displaced downward, lever 22 acts increasingly tangentially through roller 26, relative to pin 50. This causes increasing leverage upon lever 28 through the displacement of lever 22 and deflection of spring 40. Hence the force required to operate lever 22 through its full displacement is relatively constant. A single, varying cross-section flat spring 40 spans the length of housing 10. Spring 40 has a maximum effective width at fulcrum support 18, becoming narrower toward each end. The entire spring length therefore provides energy storage. Lever 28 is linked to the front of spring 40 through two possible means. By one embodiment (Fig. 10) lever 28 engages rearward extending tab 45, with tab 45 attached to the front portion of spring 40. In another embodiment (Fig. 20) lever 28 engages rearward extending tab 48 of plunger 21a. In this design (Fig. 18) , spring 40a is linked to plunger 21a through slots 49 of plunger 21a, where slots 49 are substantially aligned with tab 48 across plunger 21a. Such alignment prevents front to back motion at the plunger to spring and lever linkages from causing rotational forces upon plunger 21a. In an alternate spring design, coiled bar torsion spring 44 (Fig. 15) fits around a post within housing 10. Gap 46 is provided to allow additional clearance for lever 28. Tab 43 extends rearward to engage lever 28 similarly to tab 45 of spring 40, including the angle similar to that shown in Figure 9. Figures 5, 6, 7 & 8 show an action according to the first embodiment above (Figs. 9-14). However, the configurations of Figs. 15 and 19 may also be described by Figs. 5 through 8. In Figures 5 & 8, lever 28 is lifting tab 45. Tabs 43, 45 or 48 are angled to lightly force lever 28 and tab 23 thereof into release ledges 11, respectively, and 13 in a sliding engagement. As lever 28 continues upward, the bottom surface of lever 28, including the bottom of upper release tab 23, passes above release ledges 11 and 13. The angle in tab 43, 45 or 48 then pushes lever 28 aside and the spring is free to travel downward. Lever 28 is free to move aside through wobble about the axis formed by pins 50 and 26. Spring 42 is mounted at an off angle and out of plane to the length of lever 28 and will tend to push into the page, conceptually speaking, on the back of lever 28 in Figure 3. The front of lever 28 will then move out of the page, conceptually speaking, in Figure 3, or to the right to the configuration of Figure 7. Lever 28 is then free of tab 43, 45 or 48 and not impeded by ledges 11 & 13. The mechanism may then return to the configuration of Figures 1 and 8. As the back of lever 28 rises during the return stroke, the forward end of spring 42 is pushed away by protruding cam 12 of housing 10. The forward portion of spring 42 is behind lever 28 in Figs. 1-4. Spring 42 pivots within a notch at the back edge of lever 28. This force more than counteracts the off angle force operating in Figure 7 and causes the wobble bias upon lever 28 to reverse so that the front of lever 28 will be repositioned under tab 43, 45 or 48. Lever 28 clears tab 45 between figures 7 and 8 because cam 12 does not engage spring 42 until lever 28 is beside tab 45. The resilience of the front extension of spring 42 allows spring 42 to deflect against cam 12 before lever 28 can move under tab 43, 45 or 48. Spring 42 provides a maximum handle return bias in the initial position (Figure 1) . In this manner the return spring does not resist the operator unnecessarily when the handle is squeezed inward. Upper release ledge 13 engages release surface 23. This release supplements lower release ledge 11. Upper release 13 is especially effective since it is near the furthest location from the wobble axis defined by pins 50 and 26. Release 13 thereby provides a precise control effect at the front of lever 28. The above release system is a passive indirect release. Lever 28 is unstable under tab 43, 45 or 48 and slides out from under the tab once lever 28 is clear above ledges 11 and 13. Light sliding pressure between lever 28 and ledges 11 and 13 causes the only friction of the release system. Loading track 24 is retained within housing 10 by the combined effect of latch 33 and integral spring 36. Pressing down on surface 29 causes loading track 24 to move downward against the bias of spring 36 to lower latch 33 out of a recess within housing 10. Loading track 24 is then free to slide rearward as shown in Figure 4. Staples 70 may then be loaded into housing 10 in front of loading track 24. Staple feeder 30 is drawn to its most forward position on loading track 24 by extension spring 31. Spring 31 is attached at one end to tab 25 at the front of loading track 24, and at the other end to extended tab 32 of feeder 30. Flared tab 34 of feeder 30 (Fig. 25) fits within and below rearward extending tab 27 (Fig. 23) of loading track 24 in the position of Figure 4. Track 24, spring 31 and feeder 30 are held together this way to aid in pre-asse bly. Nose piece 81 guides staples as they are ejected and prevents wear from staples contacting the zinc housing. Shock absorber 83 limits the travel of the spring/plunger assembly. There has been described here and above a novel fastening device. Those skilled in the art may now make numerous uses of the teachings of the present invention without departing from the spirit and teachings of the present invention which are defined solely by the scope of the following claims.

Claims: CLAIMS WHAT IS CLAIMED IS: 1. A fastening device comprising: . a housing body to support and guide functional components; a fastener guide track attached to said housing near a bottom thereof, to guide fasteners toward a front of said housing; a plunger located toward the front of said housing, said plunger oriented to expel objects on said fastener guide track out of said fastening device; a spring linked to said plunger, oriented to force said plunger toward the bottom of said housing; an actuating means linkable to said plunger such that said plunger may be raised against the bias of said spring through the motion of said actuating means; said actuating means to plunger linkage comprising an engagement, said engagement exhibiting a disengagement bias when said plunger is raised to an uppermost position upon said actuating means; said engagement held from disengaging said actuating means by an applied force of a further component of said fastening device; said applied force greater than said disengagement bias to maintain contact between said engagement and said actuating means; and said applied force being instantly removed at the uppermost point of said plunger's upward travel. 2. The fastening device as described in claim 1 in which said further component is fixedly attached to said housing body forming a release surface. 3. The fastening device described in claim 2 comprising a second further component. 4. The fastening device as described in claim 1 in which said actuating means is a lever slidably linked near the front of said housing to said spring, such slidable linkage comprising said engagement. 5. The fastening device as described in claim 4 in which: said spring is a single elongated flat torque transmitting spring of varying effective width along its length; said actuating means is free to move up and down at one end along an up and down direction of motion of said plunger and is further free to move in a second direction at said same end across the width of said flat spring at the location of said engagement; said engagement occurring upon a tab attached to and cantilevered rearwardly from the front of said flat spring, said tab angled to cause said disengagement bias in said second direction upon said actuating means. 6. The fastening device as described in claim 4 in which said spring comprises at least one coiled wire torsion spring and in which: said actuating means is free to move up and down at one end along an up and down direction of motion of said plunger and is free to move in a second direction across a component of said wire spring; said component of said wire spring comprises a rearwardly bent tab near the front of said fastening device, said tab defining one end of said wire spring and being cantilevered rearwardly from the front of said fastening device; said engagement occurs upon said tab; said tab is angled to cause said disengagement bias in said second direction upon said actuating means. 7. The fastening device as described in claim 1 in which said actuating means is pivotably, slidably and disengageably connected to said plunger; said spring is pivotably linked to said plunger; said actuating means to plunger connection comprises said engagement and occurs upon a rearwardly cantilevered tab of said plunger, said tab angled to cause said disengagement bias. 8. The fastening device as described in claim 1 in which said actuating means is biased by a second spring, said second spring operating to bias said actuating means toward said engagement through a particular range of angular positions of said actuating means. 9. The fastening device as described in claim 8 in which said second spring exerts a return force to cause said actuating means to return to an initial position, said return force being greatest when said actuating means is in said initial position and least when said actuating means is displaced from said initial position. 10. The fastening device as described in claim 7 in which said spring is a flat spring and said spring to plunger connection occurs at multiple, separate locations; said actuating means to plunger connection occurs at essentially one location; said plunger connections thereby numbering at least three, and being substantially aligned across the width of said plunger. 11. A fastening device comprising: a housing body to support and guide functional components; a spring biased plunger toward the front of said housing oriented to expel fasteners stored within said housing; an operating lever pivoted toward the rear of said housing and positioned substantially above said housing, said operating lever linked to said plunger; a hand grip opening through said housing, elongated from front to back and located substantially toward the front of said housing; said housing exhibiting a substantially cantilevered profile along at least one portion of its rear face such that a portion of said housing extends rearward beyond a portion immediately below. 12. The fastening device as described in claim 11 in which said hand grip opening is defined by two distinct gripable regions: a forward section to receive the index finger of a gripping hand and a rearward section to receive the three remaining fingers, said distinct regions separated by a finger stop structure component of said housing _. 13. A fastening device comprising: a housing having a front end with finger openings, a bottom, and an internal wall; a vertical track having a base coextensive with the housing bottom, and located at the front end of the housing; a plunger slidably disposed within the vertical track; an ejection opening in the housing bottom at the base of the vertical track; a wobble lever having a front end and a back end, hingeably attached to the internal wall at a first pin, wherein the back end includes an open slot; a roller linkage disposed within the open slot; a handle lever having a distal end and a proximal end, wherein the proximal end is hingeably attached to the internal wall, and includes a bearing surface engaging the roller linkage; a lateral pressure spring attached to the internal wall and the back end of the wobble lever, biasing the front end of the wobble lever in a first vertical direction; a flat spring pivoting on the internal wall linked to the front end of the wobble lever through an angled tab to bias the front end in a first lateral direction, and biasing the front end of the wobble lever in the first vertical direction, and wherein the front end of the flat spring engages the plunger; a release ledge disposed on the internal wall near the front end of the wobble lever, laterally positioning the front end of the wobble lever in a second lateral direction that has an opposite sense to the first lateral direction; a means for feeding fasteners, disposed in the housing placing a fastener at the base of the vertical track; wherein depressing the distal end of the handle lever displaces the back end of the wobble lever in the first vertical direction by transfer of force through the roller linkage; wherein the displacement of the wobble lever pivots the front end thereof in a second vertical direction having an opposite sense to the first vertical direction, and simultaneously displacing the plunger in the second vertical direction; wherein continuous displacement of the front end of the wobble lever slides the front end thereof out of engagement with the release ledge and the angled tab forces the front end of the wobble lever in the first lateral direction disengaging the front end of the wobble lever from the flat spring; wherein the released flat spring moves in the first vertical direction and simultaneously moves the plunger in the first vertical direction, and the plunger striking a fastener in the vertical track and ejecting the fastener out of the housing through the ejection opening; wherein the lateral pressure spring biases the back end of the wobble lever in the first lateral direction and pivoting the front end of the wobble lever in the second lateral direction; and wherein the lateral pressure spring biases the front end of the wobble lever in the first vertical direction, pivoting the back end of the wobble lever in the second vertical direction and the wobble lever slidably and resiliently engaging a return cam thereby displacing the front end of the wobble lever in the first lateral direction, positioning the front end of the wobble lever in engagement with the front end of the flat spring. 14. The fastening device according to claim 13, wherein the flat spring has a wide middle section and narrow ends. 15. The fastening device according to claim 13, wherein the means for feeding fasteners further comprises a loading track containing fasteners slidably inserted inside the bottom of the housing, and the loading track includes a latch engaging a catch at the bottom of the housing, the loading track including a cantilevered spring biasing the latch into the catch. 16. The fastening device of claim 13, wherein the lateral pressure spring further comprises a coiled torsion spring. 17. The fastening device of claim 13, wherein the internal wall further comprises a second release ledge disposed near the front end of the wobble lever releasably engagaing the front end. 18. A fastening device comprising: a housing having a front, back, and bottom; a fastener guide track slideably attached to said housing near said bottom, made substantially of a sheet metal form; a further element slideable along said guide track, biased to press against fasteners upon said guide track to bias said fasteners to move along said guide track; said guide track having a first and second position, said first position being along the bottom of said housing, said second position extending rearward of said housing; said guide track held from sliding out of said first position by a latching means; said latching means employing a spring engagement means; said spring comprising an integral portion of said sheet metal form. 19. A fastening device comprising: a housing having a front, back, top, bottom and first and second sides; a first lever pivoted near the back of said housing; a plunger located within said housing near the front thereof; a second lever having first and second ends linked at said first end to said first lever and releasably linked at said second end to said plunger, said second lever pivotally connected to said housing; a torque transmitting flat spring pivoting against a fulcrum within said housing and linked at one end to said plunger, said spring decreasing in cross sectional area with increasing distance along the length of said spring away from said fulcrum; one or more openings through said housing positioned to allow a single hand to grip said first lever and also to grip said housing by passing the fingers of the single hand through said openings. 20. The fastening device as described in claim 19 wherein said housing further comprises two opposing halves, said halves constructed of die cast metal. 21. A fastening tool to install fasteners by an impact blow comprising: a housing to guide and contain mechanical parts; an elongated torque transmitting spring pivoting against a fulcrum within said housing to store and release energy to install said fasteners; a lever attached to said housing and linked to said spring such that a user may displace said lever and energize said spring; said spring being of a substantially constant thickness flat design and having a cross-sectional area that substantially decreases with increasing distance along the length of said spring away from said fulcrum. 22. A fastening tool for installing fasteners by an impact blow comprising: a housing to guide and contain mechanical parts; a lever pivotally attached within said housing; an elongated cylindrical roller contacting said lever within said housing; a further element of said fastening tool pressing against said lever through a linkage comprising said cylindrical roller; said further element spaced from said lever by the diameter of said cylindrical roller at the location of said linkage; said cylindrical roller rotating between said further element and said lever when said further element is moved relative to said lever in a direction perpendicular to the long axis of said cylindrical roller. 23. The fastening tool described in claim 22 wherein said cylindrical roller contacts said lever at a first contact surface upon said lever; said cylindrical roller contacts said further element at a second contact surface upon said further element; said first contact surface remains parallel to said second contact surface as said further element is moved relative to said lever. 24. The fastening tool described in claim 23 wherein at least one of said first and said second contact surfaces describes a curve in a direction perpendicular to the long axis of said cylindrical roller. 25. The fastening tool described in claim 23 wherein said first and second contact surfaces feature orthogonal extensions to limit motion of said cylindrical roller; said extensions causing said cylindrical roller to be entirely contained radially for a particular position of said further element relative to said lever.

Inventors: MARKS JOEL S, MARKS, JOEL, S.
Applicants: WORKTOOLS INC, WORKTOOLS, INC.
Application year: 1994
Main classification: B25C5
IPC codes: B25C5